The general objectives of this project are to define the biochemical and antigenic parameters of EIA virus in order to clarify its relationships to the RNA tumor virus group; and, to evaluate the function of the immune system during EIA infection in order to explain the mechanisms of persistence in vivo. The objectives for the current year were to more clearly define the reaction product of the reverse transcriptase (RT) enzyme and determine the physical properties of the EIA genome, to determine the number and molecular weights of the proteins of the EIA virion, to study possible cross-reactions with other RNA tumor viruses, to define more clearly the kinetics of the humoral and cellular immune responses to viral-induced cell surface antigens. BIBLIOGRAPHIC REFERENCES: Banks, K.L. and McGuire, T.C. Regulation by Antibody of Phytolectin Induced Lymphocyte Proliferation. I. Evidence for Two Mechanisms of Suppression. J. Immunol. 114:1307-1313, 1975. McGuire, T.C. Equine Infectious Anemia: Suppression of Synthesis of an IgG Subclass in Persistent Viral Infection. Immunol. 30:17-24, 1976.